The invention relates to a ball throwing apparatus which is able to accurately throw a ball or balls for baseball, softball, tennis, Ping-Pong and the like at the predetermined speed, and at a predetermined angle to any selected direction.
The machine for throwing balls for baseball is well known as a pitching machine. Such a machine can be classified into three kinds.
(1) A machine which throws a ball from a cylinder by compressed air or by the action of a compression spring. In this machine, the ball can be thrown out with an accurate control. However, it is difficult to give rotation, i.e.--spin, to the ball for curving it in the desired direction. Also, a large compression force is required to give the ball a high speed. Accordingly, since the machine has a defect in that it is large in size, it is presently not used very much.
(2) A machine which throws the ball by means of friction, that is the ball is introduced between two tires which are rotated mutually in opposite directions by a motor. The machine is of a simple construction, and used widely since it has advantages in that the direction of curve of the ball can be varied by changing the extent of rotation of both tires, the speed of the ball can be varied by varying the mean rotation speed of these tires, and the spin speed i.e.--the rotation of the ball, can be varied by means of the difference between rotation speeds of the two tires. However, it has the following defects; (a) as the ball is deformed between the two tires, a large force has to be applied to the ball at the instant the ball passes through the contact point of these tires; (b) the ball is heavily worn due to the large instantaneous friction force which acts on it; (c) as the wear of the ball reduces the roughness of the surface of the ball, the speed of the ball is lowered; and (d) since the direction of travel of the ball is delicately affected by the adhesive power of the tires with respect to the ball at the moment it leaves the tires, the ball is difficult to control. In the case of tennis ball whose surface is napped, it is easily worn away. The machine is also difficult to use for pitching a baseball for batting practice in which the ball must be thrown a long distance at a high speed.
(3) Ball throwing machine utilizing energy stored by a cam and spring. The mechanism of this is as follows. An arm is driven by an electric motor. Through a cam on a rotation axis, the energy is stored by a spring. After the cam passes through the lower dead point, the stored energy is transmitted for rotating the arm. The ball to be thrown is received in a bowl-like ball receptacle in a nearly static state and then the arm is swung. The ball is thrown out from the bowl by the centrifugal force and made to travel in the tangential direction of the circle of rotation at the time point of being thrown away. Thus, the mechanism of the machine is so simple that the machine is widely used.
However, it has some defects which will be described in the following: (a) The ball leaves the arm when the ball rolls out of the ball receptacle due to the centrifugal force caused by the rotation of the arm, the angle of rotation of the arm at this instant is delicately affected by the angular acceleration of the rotation of the arm, i.e. the strength of the spring, the frictional force of the ball receptacle and the like. Therefore, the ball is apt to be controlled inaccurately; (b) since the ball can not be spun, it can not be curved; (c) the speed of the ball restricted by the size of the compression spring. Therefore the ball can not be thrown at a high speed; (d) After the ball is thrown out, a large oscillation may occur on the machine. Accordingly, it must be firmly fixed on the ground, and therefore it can not be arbitrarily moved around when used outdoors.
The three kinds of apparatus described above utilize an electric motor, requiring an electric power source. These apparatus can therefore not easily be used out of doors where such a power source is not normally available.
In the future, it will be necessary to train baseball, tennis or Ping-Pong players through the use of automatic ball throwing apparatus with a control device including a computer operating in accordance with a stored program.
However, according to any one of these prior art apparatus, it is difficult to automate the direction and the speed of the thrown ball as well as the direction and the extent of the curve of ball.